Method and apparatus for providing voice call in mobile communication system and system thereof

ABSTRACT

A method, performed by a mobile management entity (MME), for providing a voice call service to a user equipment (UE) in a mobile communication system and the MME are provided. The method includes sending, to an evolved node B (eNB), a first message for paging to provide the voice call service to the UE; receiving, from the eNB, a second message including a cause associated with a domain change from a packet switching (PS) domain to a circuit switching (CS) domain; and sending, to a gateway in the PS domain, a third message for requesting suspension of a bearer to provide a service for the UE.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 14/327,113, filed on Jul. 9, 2014, which is aContinuation Application of U.S. patent application Ser. No. 12/465,364,filed on May 13, 2009 and issued as U.S. patent Ser. No. 8,792,417 onJul. 29, 2014, which claims priority under 35 U.S.C. §119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onMay 13, 2008 and assigned Serial No. 10-2008-0044208, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a mobile communicationsystem, and more particularly, to a method and apparatus for providingvoice calls in a heterogeneous mobile communication system and a systemthereof.

2. Description of the Related Art

A mobile communication system has been developed that allows users tocommunicate without geographic restriction. Such a mobile communicationsystem has evolved from an early system that provides only the simplevoice communication services into an advanced system that can providehigh-speed data services, and packet-based voice services such as VoiceOver Internet Protocol (VoIP).

In addition, the mobile communication system has developed from aCircuit Switching (CS) system that provides basic voice services andlower-speed data services, to a Packet Switching (PS) system that offershigh-speed packet data services. The CS-based mobile communicationsystem may include a 2^(nd) Generation (2G) system and a 3^(rd)Generation (3G) system. The 3G system may provide higher-speed dataservices. Because many users desire to receive much higher-speed dataservices, there is an increasing need for systems that have progressedfrom the 2G and 3G systems. To meet the need, a Long TermEvolution/System Architecture Evolution (LTE/SAE) system is currentlyunder development.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present inventionprovides a method and apparatus for supporting CS-domain services usingother mobile communication systems in a PS-domain mobile communicationsystem that provides IP services, and a system thereof.

Another aspect of the present invention provides a method and apparatusfor maintaining a registered state of a User Equipment (UE) in a PSdomain while the UE is receiving a voice service, or a voice callservice, in a CS domain, and a system thereof.

A further aspect of the present invention provides a method andapparatus for suspending a packet data service being provided over a PSdomain when a UE has switched from the PS domain to a CS domain toreceive a voice call service, and a system thereof.

According to an aspect of the present invention, a method, performed bya mobile management entity (MME), for providing a voice call service toa user equipment (UE) in a mobile communication system is provided. Themethod includes sending, to an evolved node B (eNB), a first message forpaging to provide the voice call service to the UE; receiving, from theeNB, a second message including a cause associated with a domain changefrom a packet switching (PS) domain to a circuit switching (CS) domain;and sending, to a gateway in the PS domain, a third message forrequesting suspension of a bearer to provide a service for the UE.

According to another aspect of the present invention, a mobilemanagement entity (MME) for providing a voice call service to a userequipment (UE) in a mobile communication system is provided. The MMEincludes a transceiver for transmitting and receiving messages; and acontroller configured to control the transceiver to transmit, to anevolved node B (eNB), a first message for paging to provide the voicecall service to the UE, control the transceiver to receive, from theeNB, a second message including a cause associated with a domain changefrom a packet switching (PS) domain to a circuit switching (CS) domainand control the transceiver to transmit, to a gateway in the PS domain,a third message requesting suspension of a service being provided to theUE in the PS domain.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following description whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a configuration of a mobilecommunication system with a CS domain and a PS domain, to which anembodiment of the present invention is applied;

FIG. 2 is a flow diagram illustrating a CS-domain service method in themobile communication network of FIG. 1;

FIG. 3 is a flow diagram illustrating a CS-domain service method in amobile communication network, according to an embodiment of the presentinvention;

FIG. 4 is a flowchart illustrating an operation of an MME, according toan embodiment of the present invention;

FIG. 5 is a flowchart illustrating an operation of an MME when it shouldsend a Paging message to a UE, according to an embodiment of the presentinvention;

FIG. 6 is a flowchart illustrating an operation of an eNB when it shouldsend a CS Paging message to a UE, according to an embodiment of thepresent invention

FIG. 7 is a flowchart illustrating an operation of an eNB when itreceived a first message from a UE in an idle state, according to anembodiment of the present invention;

FIG. 8 is a flow diagram illustrating a CS-domain service method when avoice call is received in a 3GPP2 CDMA2000 1× CS network, according toan embodiment of the present invention;

FIG. 9 is a flowchart illustrating an operation of a UE, according to anembodiment of the present invention;

FIG. 10 is a block diagram of an eNB, according to an embodiment of thepresent invention;

FIG. 11 is a block diagram of an MME, according to an embodiment of thepresent invention; and

FIG. 12 is a block diagram of a UE, according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described in detail withreference to the accompanying drawings. The same or similar componentsmay be designated by the same or similar reference numerals althoughthey are illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present invention.

The terms and words used in the following description and claims are notlimited to their dictionary meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of embodiments of the presentinvention are provided for illustration purpose only and not for thepurpose of limiting the invention as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

In the following description, the embodiments of present inventionprovide a method, apparatus and a system for providing a mobile networkservice, which was being provided from a heterogeneous mobilecommunication system over a CS domain and a PS domain, to a UE in anevolved mobile communication system that provides only the PS domain.

An evolved mobile communication network, according to embodiments of thepresent invention, sends a request message requesting locationregistration for a UE to a legacy or previous mobile communicationnetwork that provides a CS domain, thereby notifying the legacy mobilecommunication network of the current location of the UE in the evolvedmobile communication network.

As used herein, the term “evolved mobile communication network” refersto a mobile communication network providing packet data services over aPS domain, like Long

Term Evolution (LTE). The term “legacy mobile communication network”means a 2G or 3G mobile communication network providing the legacy CSdomain, like Wideband Code Division Multiple Access (W-CDMA), CodeDivision Multiple Access (CDMA) network, or Global System for MobileCommunication (GSM).

When a voice call is received at a legacy mobile communication network,the legacy mobile communication network notifies a registered evolvedmobile communication network of the receipt of the voice call so that aUE may switch to the legacy mobile communication network and receive thevoice call over the legacy mobile communication network. When a UE sendsa voice call over the legacy mobile communication network, the UEreceives information about the legacy mobile communication network fromthe evolved mobile communication network. Based on the receivedinformation, the UE switches to the legacy mobile communication networkand sends the voice call over the legacy mobile communication network.

As the service being provided in the evolved mobile communicationnetwork transitions to an idle state, the evolved mobile communicationnetwork maintains the state of the UE even while the UE is receiving thevoice call service in the legacy mobile communication network.

FIG. 1 illustrates a configuration of a mobile communication system witha CS domain and a PS domain, to which the present invention is applied.

Referring to FIG. 1, a UE 101 is connected to a phone call service overan IP network. Reference numeral 102 indicates a Core Network (CN) or aNon-Access Stratum, and an Access Network (AN) or an Access Stratum, ina General Packet Radio Service/Universal Mobile TelecommunicationsSystem (GPRS/UMTS), which is a European 2.5^(th) generation or 3^(rd)generation mobile communication system.

An Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 103, anAll-IP based core network, manages radio access. A Mobility ManagementEntity (MME) 110 takes charge of authentication and registration for theUE 101, when the UE 101 accesses a mobile communication network throughthe E-UTRAN 103. Further, the MME 110 handles a service request from theUE 101, and guarantees mobility of the UE 101 when the UE 101 travelsbetween Node Bs in the E-UTRAN 103.

A Serving Gateway (S-GW) 112 provides a bearer service for delivering auser's service data packet, including voice packet information, to theE-UTRAN 103.

A Packet Data Network Gateway (P-GW) 114 assigns an IP address to the UE101 that accessed the mobile communication network, thus providing IPconnectivity. A merger of the MME 110, the S-GW 112, and the P-GW 114 iscalled an Evolved Packet Core Network (EPC).

An enhanced Mobile Switching Center/Visited Location Register (MSC/VLR)105 represents a mobile switching center of the 2G or 3G mobilecommunication network. MSC is divided into a Gateway MSC (GMSC) 106 andthe MSCNLR 105. The MSCNLR 105 is an MSC that actually provides servicesto the UE 101, and the GMSC 106 serves to deliver a call signal to theMSCNLR 105 to which the UE 101 is connected. The MSCNLR 105 is connectedto the MME 110 via an SGs interface, for interworking with the EPC. TheMSCNLR 105 sends a UE paging request to the MME 110 via the SGsinterface, and receives a location registration request for the UE 101.

A Serving GPRS Support Node (SGSN) 109 is an entity that providesPS-domain services to the UE 101 in a UTRAN (UMTS Terrestrial RadioAccess Network)/GERAN (GSM/EDGE Radio Access Network) network 102.

A Home Location Register/Home Subscriber Server (HLR/HSS) 113 stores andprovides information about users who subscribed to the service providerrunning the mobile communication network, and the current location andregistered state information of UEs.

When a UE has switched from the LTE/SAE system to a 2G network toreceive a voice call, the currently accessed PS-domain service may besuspended in the LTE/SAE system if the UE cannot continue to enjoy thePS-domain service in the 2G network, which was provided in the LTE/SAEsystem. If data heading to the UE is received at the LTE/SAE system, theLTE/SAE system may deregister the connection, determining that the UE isout of the service area.

FIG. 2 is a flow diagram illustrating a CS-domain service method in themobile communication network of FIG. 1.

Referring to FIG. 2, in step 250, an MSC/VLR 201, which has received avoice call over a CS domain, sends a CS Paging Request message to an MME203 that is servicing a UE 209, determining that the UE 209 is currentlyconnected to an undepicted EPC via an eNB 207 in an E-UTRAN 103. Whenthe UE 209 is located in a cell supporting the CS domain, the MSCNLR 201directly pages the UE 209, and when the UE 209 is located in an E-UTRANnetwork, the MSCNLR 201 sends a paging request for the UE 209 to the MME203. The CS Paging Request message includes a CN Domain Indicatorrequesting a connection to the CS domain. Upon receipt of the CS PagingRequest message, the eNB 207 in the E-UTRAN 103 sends, if needed, arequest for neighbor cell information to the UE 209 and determines atarget cell to which it will switch the UE 209, according to informationresponded by the UE 209 or the information previously set in thenetwork, in step 252.

When an E-UTRAN in the target cell, to which the UE 209 will switch,cannot support the PS services, which the UE 209 was receiving, togetherwith the CS services, the eNB 207 provides, in step 254, target cellinformation to the UE 209 using Network Assisted Cell Change (NACC),Redirection, or the like, while maintaining the PS session currentlybeing provided in an Evolved Packet System (EPS). This allows the UE 209to switch to the target cell. The EPS includes the EPC, the eNB and theUE. NACC is a technique for providing cell information of a GERANnetwork to the UE for the UE's rapid switching when the UE switches fromthe UTRAN network to the GERAN network. A technique for switching froman E-UTRAN network to a GERAN network has also recently been defined.Redirection is also a method having similar purposes, and is differentfrom NACC in terms of Radio Resource Control (RRC) signaling.

When the UE 209 switches to the target cell, the UE 209 sends, ifneeded, a Location Area Update (LAU) request message to the MSCNLR 201to provide information about its current location in step 256. The UE209 sends a Paging Response message to the MSCNLR 201 over a UTRAN/GERANnetwork 102 in step 258. In step 260, the MSCNLR 201 establishes a voicecall according to a voice call connection procedure and provides a voicecall service to the UE 209 in the legacy CS domain.

The CS-domain service method in the mobile communication network has thefollowing problems.

If a Downlink Packet Data Unit (DL PDU) is received over a PS domain instep 262 while the UE 209 is using a voice service in step 260, an S-GW211, which does not know the fact that the UE 209 is currently receivingthe voice service, sends a DL Data Notification message indicatingreceipt of the DL PDU to the MME 203 according to a normal DL PDUreception procedure in step 264. The MME 203 sends a Paging Requestmessage to the eNB 207 in the E-UTRAN 103 in step 266. However, becausethe UE 209 is currently receiving the voice service in coverage of theUTRAN/GERAN network 102, the UE 209 cannot receive a Paging Requestmessage from the eNB 207 in the E-UTRAN 103 in step 268. In step 270, ifthe MME 203 determines failure of paging because it has failed toreceive a response to the Paging request, the MME 203 performs aprocedure for releasing the registered state of the UE 209 in the PSdomain. Therefore, when the UE 209 accesses the E-UTRAN 103 aftercompleting the voice service, the UE 209 should newly perform thePS-domain registration procedure from the beginning, and may lose allinformation about the existing PS session.

Embodiments of the present invention, described below, may be appliedwhen the same PS service as the PS service the UE was receiving in theevolved mobile communication network, such as the LET network, cannot becontinuously provided in the legacy mobile communication network such asthe WCDMA/GSM/CDMA 2000 1× network.

The evolved mobile communication system according to embodiments of thepresent invention, described below, sends a request message requestinglocation registration for a UE to the legacy mobile communication systemthat provides a CS domain, to notify the legacy mobile communicationsystem of the current location of the UE in the evolved mobilecommunication system.

When an event, such as a voice call, occurs in the legacy mobilecommunication system, the mobile communication system, according toembodiments of the present invention, notifies the registered evolvedmobile communication system of the occurrence of event so that the UEmay switch to the legacy mobile communication system and receive aservice over the legacy mobile communication system.

When the UE has moved or switched to the legacy mobile communicationsystem without a PS handover procedure by which the UE can receive, evenin the legacy mobile communication system, the same PS service as the PSservice it was receiving in the evolved mobile communication system, theevolved mobile communication system may maintain the registered state ofthe UE. In the following description, although the MSC of the mobilecommunication system providing a phone call service and the evolved corenetwork based on 3GPP will be taken as an example of the LTE/SAE system,the procedure provided by the present invention can be equally appliedeven to the mobile communication networks that use other protocols oraccess standards.

In the following description, the expression “a UE is located in aspecific domain” includes both a meaning that the UE is located in anarea of the specific domain, and another meaning that the UE accessesthe specific domain. The phrase “a current location of a UE” alsoincludes both a meaning of “an actual location of the UE” and anothermeaning of “a specific network that the UE currently accesses.” Forexample, in the specification, the expression “a UE is located in a CSdomain” includes both an expression that the UE is located in an area ofthe CS domain, and another expression that the UE accesses the CSdomain. In addition, an expression “a UE moves to a specific domain”includes a meaning that the UE switches to a specific domain.

FIG. 3 is a flow diagram illustrating a CS-domain service method in amobile communication network, according to an embodiment of the presentinvention.

Referring to FIG. 3, in step 350, an MSC/VLR 301, which has received avoice call over a CS domain, sends a CS Paging Request message to an MME303 that is servicing a UE 309, determining that the UE 309 is currentlyconnected to an LTE/SAE system via an eNB 307 in the E-UTRAN 103. TheMSC/VLR 301 can determine if the UE 309 is connected to the LTE/SAEsystem when the UE 309 performs registration in the MSC/VLR 301 over theLET network. The CS Paging Request message includes a CN DomainIndicator requesting a connection to the CS domain.

Upon receipt of the CS Paging Request message, the eNB 307 in theE-UTRAN 103 sends, if needed, a request for neighbor cell information tothe UE 309 and determines a target cell to which it will switch the UE309, according to information responded by the UE 309 or the informationpreviously set in the network, in step 352.

When the target cell to which the UE 309 will switch cannot support PSservices together with the CS services, the eNB 307 provides, in step354, the target cell information, which is equal to information aboutthe channel the UE 309 will use in the target cell, to the UE 309 usingNACC while maintaining the PS session currently being provided in theLTE/SAE network. This allows the UE 309 to switch to the target cell andreceive a service. Step 354 is possible even with the Redirection methodas described above. In step 356, the eNB 307 in the E-UTRAN 103 sends tothe MME 303 a Domain Change Report message indicating that the UE 309has switched to an area where it cannot provide PS services (i.e. thatthe UE 309 is out of the EPS network). The Domain Change Report messageincludes an indicator indicating that the UE 309 is currently located inthe CS domain. In addition, the Domain Change Report message includes aCause indicating that the Domain Change Report message is sent becausethe UE 309 cannot receive PS services. In the present invention, theindicator indicating that the UE 309 is currently located in the CSdomain is a CN Domain Indicator. The CN Domain Indicator is set toindicate “CS” and transmitted through the Domain Change Report message.Also, the UE 309 may directly send a PS Session Preservation message tothe MME 303 to request suspension of the PS session in step 358.

The embodiment of the present invention proposes, as shown in step 359,two different methods in which the MME 303 can determine that the UE 309has switched to the CS domain. The eNB 307 may determine whether the UE309 is located in the CS domain and provide the resulting information tothe MME 303 using the Domain Change Report message as in step 356, orthe UE 309 may directly provide its location information to the MME 303using the PS Session Preservation message as in step 358. In thisspecification, the Domain Change Report and the PS Session Preservationmessage, which are sent to the MME 303 in step 359, are referred to as“report messages.”

Through the process in step 359, the MME 303 may determine that the UE309 cannot receive packet services over the PS domain because the UE 309is currently receiving a voice call service in the CS domain.

A similar process may apply to another case where the UE 309 sends avoice call, in addition to the foregoing case where the UE 309 receivesa voice call. When the UE 309 sending a voice call sends a request foran outgoing voice call to the LTE/SAE network, the UE 309 receivesinformation used to switch to the target cell via the E-UTRAN 103 as instep 352.

The MME 303, which received the message in step 356 or 358, indicatesthat the UE 309 is registered in the PS domain of the EPC network. TheUE 309 is in an idle state where a radio connection is not maintained,and cannot receive a response to a Paging request for data reception,i.e. the EPS service is suspended. That is, in step 359, the MME 303knows that it cannot receive a Paging Response message from the UE 309,using the indicator in the message received from the UE 309 or the eNB307. Accordingly, the EPS sends no Paging message to the UE 309.Further, in order to avoid unnecessarily paging the UE 309 due toadditional data reception, the MME 303 sends a Service Change Requestmessage for preventing data reception to a GW 311 such as an S-GW and aP-GW, or sends a Suspend Request message for requesting the GW 311 toset a service state of the UE 309 as a suspended state, in step 360.Thereafter, a DL PDU received in step 362 is discarded in the GW 311such as S-GW or P-GW in step 364, and the S-GW 112 does not send a DLData Notification message requesting UE paging, to the MME 303.

Concerning step 360, the same function may be achieved using an UpdateBearer Request message instead of the Suspend Request message. If themaximum transmission/reception rate for a bearer is set to 0 Kbps usingthe Update Bearer Request message, data transmission/reception can beprevented in the P-GW 114. The Update Bearer Request message may includea Cause indicating that the Update Bearer Request is sent because the UE309 cannot receive PS services. When the Cause is included, the GW 311may internally set the UE's state.

If the UE 309, which received the target cell information in step 354,switches to the target cell, the UE 309 sends, if needed, a LocationArea Update request message to the MSC/VLR 301 to notify the currentlocation (UE is currently located in the CS domain) of the UE 309 instep 366, and sends a Paging Response message to the MSC/VLR 301 overthe UTRAN/GERAN network 102 in step 368. Step 368 can be omitted for anoutgoing call. In step 370, the MSC/VLR 301 establishes a voice callaccording to a voice call connection procedure in the legacy CS domain,and provides a voice call service to the UE 309. Even though there is aDL PDU received over the PS domain in step 362 while the GW 311 isproviding a voice call service, no paging request occurs in the PSdomain because the DL PDU is discarded in step 364.

When the UE 309, which has terminated the voice call service, returns tothe E-UTRAN network in step 372, the UE 309 sends a Non-Access Stratum(NAS) message such as a Tracking Area Update message to the MME 303 overthe EPC network in step 374. Then the MME 303 determines that PSservices are available. Also, when the eNB 307 in the E-UTRAN 103 hasreceived any message from the UE 309, the eNB 307 may inform the MME 303of the receipt in step 376. The MME 303, which received the NAS messagesuch as a Tracking Area Update message in step 374 or received themessage associated with the UE 309 from the eNB 307 in the E-UTRAN 103in step 376, releases a suspended state, if any, where the current stateof the UE 309 is registered in the PS domain but a Paging message cannotbe received. The MME 303 sends a Data Reception Resume Request messageto the GW 311, such as an S-GW and a P-GW, in step 378 so that a DL PDUcan be provided to the UE 309 in step 380 after step 378. The MME 303sends a Resume Request message as an example of the Data ReceptionResume Request message to release the suspended state of the UE 309 inthe GW 311, or sends a Bearer Update Request message to reset themaximum transmission/reception rate for the bearer belonging to the UE309 to a previous value for the service suspended state.

FIG. 4 is a flowchart illustrating an operation of an MME 303, accordingto an embodiment of the present invention. In step 402, the MME 303receives a CS Paging Request message from an MSCNLR 301. In step 404,the MME 303 forwards the CS Paging Request message to an eNB 307 in anE-UTRAN. Thereafter, if the MME 303 receives a Domain Change Reportmessage indicating that the UE 309 has switched to a target cell notsupporting PS services, from the eNB 307 in the E-UTRAN, or receives aPS Session Preservation message from the UE 309 in step 406, the MME 303sets the UE 309 to a suspended state in step 408. In order to avoidunnecessarily sending a Paging message to the UE 309 due to receipt of aDL PDU, the MME 303 additionally sends a Suspend Request message to a GW311 in step 410, setting a state in which the UE 309 cannot receivedata. Alternatively, as described in FIG. 3, the set maximumtransmission/reception rate of an Update Bearer Request message may bechanged to perform the same function as the Suspend Request message.

FIG. 5 is a flowchart illustrating an operation of an MME 303 when itshould send a Paging message to a UE 309, according to an embodiment ofthe present invention.

If a situation occurs in step 500, in which the MME 303 should send aPaging message to the UE 309, the MME 303 determines in step 502 whetherthe UE 309 is now in a state where it cannot receive a Paging message.If it is determined in step 502 that the UE 309 is in the state where itcannot receive a Paging message, the MME 303 stores the informationindicating existence of a pending Paging message to the UE 309 withoutsending any Paging message, in step 504. On the contrary, if it isdetermined in step 502 that the UE 309 is in the state where a Pagingmessage can be received, the MME 303 pages the UE 309 by sending aPaging message to an eNB 307 in an E-UTRAN in step 506.

FIG. 6 is a flowchart illustrating an operation of an eNB 307 when itshould send a CS Paging message to a UE 309, according to an embodimentof the present invention.

In step 602, the eNB 307 receives a CS Paging Request message from anMME 303 or the UE 309 (in case of an outgoing call). Herein, the CSPaging Request message commonly refers to a Paging Request messagereceived from a CDMA2000 network. In step 604, the eNB 307 gathersinformation about a target cell to which the UE 309 will switch, from atarget network. In step 606, the eNB 307 determines a PS handoverdepending on whether the target cell supports a PS handover. If the PShandover is possible, the eNB 307 sends, in step 608, a request for a PShandover procedure to the MME 303 regarding the PS service that the UE309 is receiving. In step 610, the eNB 307 commands the UE 309 to switchto a CS domain of the target cell. Examples of such a command mayinclude handover command, NACC, Redirection, etc. In the presentinvention, any other messages can be used as messages commanding theswitching to the CS domain. In step 612, the eNB 307 sends the MME 303 aDomain Change Report message indicating that the UE 309 has switched tothe CS domain.

FIG. 7 is a flowchart illustrating an operation of an eNB 307 when itreceived a first message from a UE 309 in an idle state, according to anembodiment of the present invention.

In step 702, the eNB 307 receives a message from the UE 309 in an idlestate, which was not connected to the eNB 307. In step 704, the eNB 307requests UE context information for communication with the UE 309, fromthe MME 303. In step 706, the eNB 307 determines that the UE 309 has nowreturned from the CS domain to the PS domain, based on the recent domaininformation of the UE 309, contained in the UE context information. Instep 706, the eNB 307 may determine if the UE 309 was located in the CSdomain by checking if the CN domain indicator is set as “CS domain.” Ifit is determined in step 706 that the UE 309 has returned from the CSdomain to the PS domain, the eNB 307 sends a Domain Change Reportmessage indicating that the UE 309 has returned to the PS domain, to theMME 303 in step 708.

FIG. 8 is a flow diagram illustrating a CS-domain service method when avoice call is received in a 3GPP2 CDMA2000 1× CS network, according toan embodiment of the present invention.

A UE 809 has been registered in a CDMA2000 1× CS network via an E-UTRAN807, using a tunneling message that passes through an MME 803.

When an MSC 801, which has received an incoming call for the UE 809,sends a 1× Paging message over a 1× CS InterWorking Solution (IWS) orHigh Rate Packet Data (HRPD) Access Network (AN) 805 in step 850, the 1×CS IWS/HRPD AN 805 directly transfers the 1× Paging message to the MME803 using a tunneling message in step 852. Upon receiving the tunnelingmessage from the 3GPP2 1× CS network, the MME 803 forwards the received1× Paging message to the UE 809 using a NAS tunneling message in step854. When a 3GPP2 message delivered by the NAS message is a 1× Pagingmessage, an indication that the tunneling message is a CS Paging messagecan be made so that an eNB in the E-UTRAN 807 may have no need to checkthe NAS message. When there is no such indication, the eNB checks allcontents of a NAS message carrying 1× messages to determine if the NASmessage is a Paging Request message. In step 854, the MME 803 pages theUE 809 by sending the 1× Paging message. Step 854 is a procedure thatshould be performed in advance to provide a voice call, or a CS-domainservice, to the UE 809.

When the message being delivered is a 1× Paging Request message or whenit is determined that the UE 809 has switched to a target cell in a CSdomain, the eNB in the E-UTRAN 807 sends a Domain Change Report messageto the MME 803 in step 856 a, indicating that the UE 809 has switched tothe CS domain. Also, the UE 809 may directly send a PS SessionPreservation message requesting suspension of a PS session, to the MME803 in step 856 b. Upon receiving the message in step 856 a or 856 b,the MME 803 indicates that the UE 809 is in a state where it cannotreceive packet services. In step 858, the MME 803 sends a SuspendRequest message to a GW 811 to change a state of the UE 809 in the GW811 to a state in which packet transmission/reception is suspended,thereby making it possible for the UE 809 to transmit/receive no morepacket data while receiving a CS service in the CS service.

Similarly, there are two methods in FIG. 8, by which the MME 803 candetermine that the UE 809 is in the CS domain. The two methods justcorrespond to steps 856 a and 856 b. The MME 803 receives the DomainChange Report message from the E-UTRAN 807 in step 856 a, or the PSSession Preservation message from the UE 809 in step 856 b, therebydetermining that the UE 809 cannot receive PS-domain services as it iscurrently located in the CS domain. Through step 857, the MME 803 maydetermine that the UE 809 cannot currently receive PS-domain services.In the meantime, in step 860 and 862, the UE 809, which has switched tothe CDMA2000 1× CS domain, receives a voice call service through anincoming/outgoing call connection procedure based on the 1× CS signalingprocedure with the MSC 801 in the CDMA2000 1× network as in the existingprocedure. Steps 864 to 878 are equivalent to step 362, step 364, andsteps 370 to 380 of FIG. 3.

FIG. 9 is a flowchart illustrating an operation of a UE 309 (or 809),according to an embodiment of the present invention.

In step 900, the UE 309 (or 809) accesses a PS domain and receives aservice over the PS domain. In step 902, the UE 309 (or 809) determinesif a CS-domain service such as a voice call service is needed. Forexample, upon receiving a message such as a Paging message from a CSdomain, the UE 309 (or 809) may determine that a CS-domain service isneeded. If it is determined in step 902 that a voice call service isneeded, the UE 309 (or 809) switches to the CS domain according to apredetermined handover procedure in step 904. In step 906, the UE 309(or 809) requests an MME 303 (or 803) to suspend a PS-domain service asin step 358 of FIG. 3 or step 856 b of FIG. 8. After requesting thesuspension of the PS-domain service in step 906, the UE 309 (or 809)provides a voice call service in step 908, and then switches to the PSdomain in step 910 when the voice call service is terminated.

FIG. 10 is a block diagram of an eNB 1000, according to an embodiment ofthe present invention.

An eNB 1000 in FIG. 10 represents the eNB 307 in FIG. 3, and the eNB ofan E-UTRAN 807 in FIG. 8. In the eNB 1000, a transmission/receptionmodule 1002 receives a Paging message from an MME 303 (or 803), providesit to a controller 1004, and delivers the received Paging message to aUE 309 (or 809) under control of the controller 1004. In addition, thetransmission/reception module 1002, under control of the controller1004, sends to the MME 303 (or 803) a Domain Change Report indicatingthat the UE 309 (or 809) cannot receive PS-domain services as it hasswitched to the CS domain.

Upon receiving the Paging message through the transmission/receptionmodule 1002, the controller 1004 determines if the UE 309 (or 809) towhich it will deliver the Paging message has switched from the PS domainto the CS domain. If the UE 309 (or 809) has switched to the CS domain,the controller 1004 controls the transmission/reception module 1002 tosend the Domain Change Report message to the MME 303 (or 803). Further,the controller 1004 gathers information about a target cell for the UE309 (or 809), determines whether to perform a PS handover depending onwhether the target cell supports the PS handover, and sends/receiveshandover-related messages through the transmission/reception module 1002according to the determination result.

FIG. 11 is a block diagram of an MME 1100, according to an embodiment ofthe present invention. An MME 1100 in FIG. 11 represents the MME 303 inFIG. 3, and the

MME 803 in FIG. 8. A transmission/reception module 1102 in the MME 1100exchanges messages with network entities in each of a CS domain and a PSdomain, delivers received messages to a controller 1104, and sendsmessages created by the controller 1104. When a Paging message isreceived from an MSC 301 (or 801) in the CS domain, thetransmission/reception module 1102 in the MME 1100 delivers the receivedPaging message to the controller 1104, and the controller 1104 controlsthe transmission/reception module 1102 to send the Paging message to aUE 309 (or 809). When a message indicating that the UE 309 (or 809) hasswitched to the CS domain is received from an eNB 307 (or 807) or the UE309 (or 809) through the transmission/reception module 1102, thecontroller 1104 sets a PS-domain service for the UE 309 (or 809) to asuspended state and stores the resulting information in a memory 1106.When the MME 1100 receives a Domain Change Report message from the eNB307 (or 807) or a PS Session Preservation message from the UE 309 (or809), the controller 1104 sets the PS-domain service for the UE 309 (or809) to a suspended state and stores the resulting information in thememory 1106.

After setting the PS-domain service to the suspended state regarding theUE 309 (or 809), the controller 1104 controls the transmission/receptionmodule 1102 to send a Suspend Request message to a GW.

FIG. 12 is a block diagram of a UE 1200, according to an embodiment ofthe present invention. The UE 1200 in FIG. 12 represents the UE 309 inFIG. 3 and the UE 809 in FIG. 8.

A transmission/reception module 1202 in FIG. 12 sends/receives messageswith network entities over a radio signal, and a controller 1204receives messages through the transmission/reception module 1202,handles the received messages according to a specific procedure, anddelivers messages created by a specific procedure through thetransmission/reception module 1202. A memory 1206 stores parameters ordata created by processing of the controller 1204. In accordance with anembodiment of the present invention, the controller 1204 determines if aCS-domain service such as a voice call service is needed, whileaccessing the PS domain and receiving a service through thetransmission/reception module 1202. For example, upon receiving amessage such as a Paging message through the transmission/receptionmodule 1202, the controller 1204 may determine that the CS-domainservice is needed. If the voice call service is needed, the controller1204 switches to the CS domain according to a predetermined handoverprocedure. Further, the controller 1204 requests an MME 303 (or 803) tosend a Suspend Request message through the transmission/reception module1202 in order to request suspension of a PS-domain service.

As is apparent from the foregoing description, according to embodimentsof the present invention, a UE connected to a mobile communicationsystem not supporting a CS domain can receive a service specific to theCS domain from a heterogeneous mobile communication system that providesthe CS domain.

In addition, a UE can receive a service specific to a PS domain of itsmobile communication system from a heterogeneous mobile communicationsystem that provides the PS domain.

Further, embodiments of the present invention can prevent UE'sregistered state in a PS domain from being released after the UE ishanded over from the PS domain to the CS domain.

The present invention suspends a packet data service being provided overa PS domain to a UE that has switched from the PS domain to a CS domainto receive a voice call service, thereby preventing a waste ofresources, which may occur in the PS domain.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method, performed by a mobile management entity(MME), for providing a voice call service to a user equipment (UE) in amobile communication system, the method comprising: sending, to anevolved node B (eNB), a first message for paging to provide the voicecall service to the UE; receiving, from the eNB, a second messageincluding a cause associated with a domain change from a packetswitching (PS) domain to a circuit switching (CS) domain; and sending,to a gateway in the PS domain, a third message for requesting suspensionof a bearer to provide a service for the UE.
 2. The method of claim 1,further comprising: setting information associated with the UE to asuspended state.
 3. The method of claim 1, further comprising:receiving, from the gateway in the PS domain, a fourth messageindicating that the third message has been received in the gateway. 4.The method of claim 1, wherein the first message comprises a corenetwork (CN) domain indicator for indicating a domain where the UE islocated to receive the voice call service.
 5. A mobile management entity(MME) for providing a voice call service to a user equipment (UE) in amobile communication system, the MME comprising: a transceiver fortransmitting and receiving messages; and a controller configured to:control the transceiver to transmit, to an evolved node B (eNB), a firstmessage for paging to provide the voice call service to the UE, controlthe transceiver to receive, from the eNB, a second message including acause associated with a domain change from a packet switching (PS)domain to a circuit switching (CS) domain and control the transceiver totransmit, to a gateway in the PS domain, a third message requestingsuspension of a service being provided to the UE in the PS domain. 6.The MME of claim 5, wherein the controller is further configured to set,before transmitting the first message, information associated with theUE to a suspended state.
 7. The MME of claim 5, wherein the receiver isfurther configured to receive, from the gateway in the PS domain, afourth message indicating that the third message is received in thegateway.
 8. The MME of claim 5, wherein the first message comprises acore network (CN) domain indicator for indicating a domain where the UEis located to receive the voice call service.